Why is it that ashless 2-stroke oil can provide adequate lubrication even when it is severely diluted in fuel and has no metal-type boundary lubrication (no Zn, Mo, B, ect)?
ashless 2-stroke in a 4-stroke
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WOW! Good question and good answer.
I can see the "used once" argument for soot loading, acid build-up, ect. I can also accept this point of view for degradation products. However, film strength and viscosity of the lubricant are still much lower in 2-strokes than in 4-stroke engines. So, I am left wondering if bearings and rings require much less in the way of film strength than the valve train/cam.
If the "used once" position is accurate, then you should be able to flush a 4-stroke with 100:1 fuel/oil. It just seems to me that even the "designed for 20 wt" engines would not do well on a severly diluted 2-stroke oil.
If the "used once" position is accurate, then you should be able to flush a 4-stroke with 100:1 fuel/oil. It just seems to me that even the "designed for 20 wt" engines would not do well on a severly diluted 2-stroke oil.
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2 strokes use roller not sliding bearings.
2 stroke also has either some ester or bright stock or PIB for lubrication and anti scuff protection.
bruce
bruce
So, even at 16:1 with PIB, ester, and bright stock, how much wear should be expected after running a 4-stroke on this mix for 15 minutes (assuming that the fuel doesn't evaporate or explode)?
I am really trying to understand how a lube this thin (and without ash-type boundary lubrication) is fine for a 2-stroke while 4-strokes tend to "require" at least 20 wt (yes, I know about 5 wt for qualifying runs).
I am really trying to understand how a lube this thin (and without ash-type boundary lubrication) is fine for a 2-stroke while 4-strokes tend to "require" at least 20 wt (yes, I know about 5 wt for qualifying runs).
Am I reading this question right?
You seem to be asking not about running a 4-stroke on 2-stroke fuel, but about putting 100:1 premixed GASOLINE in your oil sump, then running the engine?!*??&%#??
You can't be serious.....
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doc
You seem to be asking not about running a 4-stroke on 2-stroke fuel, but about putting 100:1 premixed GASOLINE in your oil sump, then running the engine?!*??&%#??
You can't be serious.....
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doc
doctorr wrote: "You seem to be asking not about running a 4-stroke on 2-stroke fuel"
Correct
doctorr wrote: "but about putting 100:1 premixed GASOLINE in your oil sump, then running the engine?!*??&%#??"
Sort of...
I am not recommending the practice. I am asking why a 2-stroke can use premixed gas/oil as the only lubricant, yet it seems that the same concoction would be a really bad idea in a 4-stroke. I am granting that there are issues with TBN, contamination removal, and the explosive nature of gas. My curiosity is related to why 2-strokes can use this very thin lube without the common boundary lubricant additives. Why aren't the bearings and rings in 2-stroke engines quickly destroyed by cavitation and scuffing? If you had some sort of single pass system, would 2-stroke fuel/oil be adequate in a 4-stroke engine as the lubricant. It seems the answer should be "no!", but since it works in 2-stroke engines, why wouldn't it work in a 4-stroke.
The question is serious. I am trying to understand the difference in lubrication demands between a 2-stroke and a 4-stroke. Are bearing and rings surfaces just not as demanding as cam surfaces?
Correct
doctorr wrote: "but about putting 100:1 premixed GASOLINE in your oil sump, then running the engine?!*??&%#??"
Sort of...
I am not recommending the practice. I am asking why a 2-stroke can use premixed gas/oil as the only lubricant, yet it seems that the same concoction would be a really bad idea in a 4-stroke. I am granting that there are issues with TBN, contamination removal, and the explosive nature of gas. My curiosity is related to why 2-strokes can use this very thin lube without the common boundary lubricant additives. Why aren't the bearings and rings in 2-stroke engines quickly destroyed by cavitation and scuffing? If you had some sort of single pass system, would 2-stroke fuel/oil be adequate in a 4-stroke engine as the lubricant. It seems the answer should be "no!", but since it works in 2-stroke engines, why wouldn't it work in a 4-stroke.
The question is serious. I am trying to understand the difference in lubrication demands between a 2-stroke and a 4-stroke. Are bearing and rings surfaces just not as demanding as cam surfaces?
I don't want to get into Amsoil 100:1 or Mobil MX2T ester synthetic, but the classic conventional 2 stroke mixes have a rather heavy base oil component that generates good film strength for ring lubrication and the needle & roller bearings.
As Bruce mentioned, brightstock is a heavy, residual base oil that is very heat resistant.
And remember, 2 stroke mix oil is typically blended with deodorized kerosene or stoddard solvent to aide mixing with gasoline, so the heavy base oil component is not readily visible as it is poured out of the bottle.
As Bruce mentioned, brightstock is a heavy, residual base oil that is very heat resistant.
And remember, 2 stroke mix oil is typically blended with deodorized kerosene or stoddard solvent to aide mixing with gasoline, so the heavy base oil component is not readily visible as it is poured out of the bottle.
much of 2 stroke oil drops out of the fuel when the air fuel oil mixture is in the crankcase. some of it stays in the fuel and is burned. This is easy to see when you tear down a dirtbike engine, there is a coating of oil on the crank/piston ect.The oil eventuly gets pumped out the exhaust port especialy at high rpm.
The main lubrication difference is far less moving parts to lube and 2t oil doesn't need a lot of the additives used in 4t oil.
The main lubrication difference is far less moving parts to lube and 2t oil doesn't need a lot of the additives used in 4t oil.
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